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Implied compares in Ada Harded Conditionals documentation 

Improve the wording on optimizations that prevent compare hardening,
so as to also cover cases in which explicit compares get combined into
operations with implied compares.


for  gcc/ada/ChangeLog

	* doc/gnat_rm/security_hardening_features.rst: Mention
	optimization to operations with implied compares.
This commit is contained in:
Alexandre Oliva 2021-10-30 06:36:05 -03:00 committed by Alexandre Oliva
parent 6f449bb93b
commit 70c947e4df
1 changed files with 4 additions and 3 deletions
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7
gcc/ada/doc/gnat_rm/security_hardening_features.rst
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@ -112,14 +112,15 @@ long after boolean expressions are decomposed into separate compares,
each one turned into either a conditional branch or a compare whose
result is stored in a boolean variable or temporary. Compiler
optimizations, if enabled, may also turn conditional branches into
stored compares, and vice-versa. Conditionals may also be optimized
stored compares, and vice-versa, or into operations with implied
conditionals (e.g. MIN and MAX). Conditionals may also be optimized
out entirely, if their value can be determined at compile time, and
occasionally multiple compares can be combined into one.
It is thus difficult to predict which of these two options will affect
a specific compare operation expressed in source code. Using both
options ensures that every compare that is not optimized out will be
hardened.
options ensures that every compare that is neither optimized out nor
optimized into implied conditionals will be hardened.
The addition of reversed compares can be observed by enabling the dump
files of the corresponding passes, through command line options